1. Field of the Invention
The present invention relates to a control system for an apparatus having a permanent split capacitor (PSC) motor and more particularly to a control for an automatic washing machine having a reversing PSC motor wherein the operations of the washing machine are controlled in response to phase angles of the motor determined from sensed zero crossings of current flowing through the motor's windings when the motor is on and in response to the sensed zero crossings of residual motor generated current flowing through the motor's windings when the motor is off.
2. Description of the Prior Art
A control system for various appliances having an AC induction drive motor including an automatic washing machine is shown in my U.S. Pat. No. 4,481,786. That control system employs a ferrite core sensor having a primary winding that is formed of two turns of the drive motor's run winding, the sensor having a single turn secondary winding that forms a sense winding coupled to a motor phase monitoring circuit. The sense winding provides a signal representing a polarity change in the run winding current. The current polarity change signal is used by the motor phase monitoring circuit to provide a voltage compensated motor phase angle pulse to a microcomputer for the appliance to control various operations of the appliance. More particularly, a digital representation of the motor phase angle pulse is used by the microcomputer to monitor the starting of the drive motor by detecting a characteristic decrease in the motor phase angle representation. The motor phase angle representation is further used by the microcomputer of an automatic washing machine to determine the agitator torque which is in turn used by the microcomputer to automatically control the water level of the washing machine. An average motor torque number is also determined from the motor phase angle representation wherein the average motor torque number is used to provide an end of drain control for the washing machine.
The washer agitator torque routine (WATR) in FIG. 10 of U.S. Pat. No. 4,481,786 applies to washing machines which use a complex transmission to define the stroke angle and to convert the rotary motion of the motor into a back-and-forth, clockwise (CW) and counterclockwise (CCW) agitator motion. The motor of U.S. Pat. No. 4,481,786 rotates continuously and in a single direction during each clothes agitation period. The mid-stoke agitator torque is inferred by using the microcomputer to store the maximum and minimum motor phase number during each CW and CCW agitator stroke and compute the difference. The maximum motor phase number during each CW and CCW stroke occurs when the transmission gears are positioned such that the agitator is in hesitation. This number provides a base-line or reference motor phase number unaffected by agitator torque to which the minimum motor phase number or mid-stroke agitator torque can be compared.
The present invention applies to washing machines wherein each reversal of direction of the agitator is achieved by stopping and restarting the drive motor in the opposite direction. Washing machines of the present invention may use a transmission, but the transmission is relatively simple and provides a basic motor speed reduction and/or torque multiplication function. The direction of rotation of the motor determines the agitation direction and the angle of rotation of the motor shaft in conjunction with the transmission gear-ratio determines the agitation stroke angle. The present invention teaches how to use information from the motor electrical parameters to provide a closed-loop automatic water level control function in the absence of the above base-line or reference motor phase information as such information is not available with a washing machine having a simple, speed-reducing transmission. Also, the preferred embodiment pertains to a permanent split capacitor (PSC) drive motor as PSC motors are generally more amenable in applications requiring frequent starting, stopping and reversal of the motor rotational direction than split phase induction motors.
It has been found that automatic washing machines having reversing PSC drive motors cannot be as accurately controlled by the control system shown in U.S. Pat. No. 4,481,786 as washing machines having AC induction motors because the motor start time of a PSC motor varies not only with the size of the clothes load but with variations in the installation line voltage. More particularly, for a washing machine having a reversing PSC motor, the line voltage affects the motor start time more than the size of the clothes load. Further, the motor phase angle of a PSC motor does not change in the same manner as the motor phase angle of an AC induction motor since there is not a characteristic decrease in the phase angle of the PSC motor indicative of the motor reaching its operating speed. Another difference between washing machines having an AC induction motor and washing machines having a PSC motor is that the stroke angle and stroke rate of an agitator driven by an AC induction motor is fixed; whereas, the stroke angle and stroke rate of an agitator driven by a reversing PSC motor is variable.